1. Field of the Invention
The present invention generally relates to the field of intravascular medicine and more particularly to the field of catheters, and still more particularly to balloon catheters such as dilation catheters used for medical treatments within the body.
2. Description of the Prior Art
The use of intravascular catheters for treatment of the body is well known in the field of medicine. The use of dilation or balloon catheters has become widespread in the treatment, for example, of restrictions within the coronary blood vessels, such as stenotic lesions. In this balloon angioplasty, a catheter carrying a balloon at its distal end is guided through the blood vessel to a point adjacent the lesion. The placement of the balloon is aided by use of a fluoroscope and radiopaque elements, as well as other modern technological advances. The size and type of the balloon is generally selected by the physician based on his knowledge of the size and type of lesion. The balloon is then expanded by providing an expansion fluid from the proximal end of the catheter through a fluid lumen within the catheter to the balloon. The expanded balloon acts on the lesion in a manner to reopen at least a portion of the restricted vessel. The balloon is then deflated for removal from the body, though sometimes repeated reinflation may be deemed necessary by the physician prior to removal.
Though balloon angioplasty is well known as a safe and effective method for treatment of the vascular disease described above, there are still problems that arise during the procedure. For example, stenotic lesions often have a highly irregular cross-sectional configuration, and may vary greatly in their hardness, both of which make for difficulty in determining what size and composition of balloon to use, and how often to inflate it.
It is known in the field that if the physician can have information as to the amount of inflation the fluid has caused in the balloon under use, he can use this knowledge to increase the chance of completing a successful angioplasty while at the same time having less risk of damage to the vessel which could be caused by over-inflation or repeated reinflation of the balloon. A known way of providing the desired balloon inflation size is to monitor the pressure within the balloon during the inflation procedure, transform the measured pressure into electrical signals, conduct the signals from the body to a microcomputer outside the catheter, and provide the physician with inflation information based on the known and previously charted relationship between pressure and the inflation of the type of balloon being used.
One example of this prior art solution to the problem is shown in U.S. Pat. No. 5,171,299, issued Dec. 15, 1992 to H. A. Heitzmann et al. One of the difficulties with this solution for the problem at hand is that it is necessary to place a pressure transducer within the catheter and in contact with the interior of the balloon. Such a transducer may tend to be somewhat cumbersome in a catheter, and may have a need for special protection from the fluids it will encounter during use. Further, the process of transducing pressure to the desired electrical signal will carry some error which must be accounted for in the measurement circuitry.
Another solution to the problem used in the prior art is a catheter with an external inflation device for providing inflation fluid to the balloon. The external device carries a pressure gauge for monitoring inflation pressure in the balloon, from which data it is possible to determine the inflation level of the balloon in the manner described above.